Over recent years the interest in semiconductor nanowires has increased. In comparison with conventional planar technology nanowire based semiconductor devices offer unique properties due to the one-dimensional nature of the nanowires, improved flexibility in materials combinations due to less lattice matching restrictions and opportunities for novel device architectures. Suitable methods for growing semiconductor nanowires are known in the art and one basic process is nanowire formation on semiconductor substrates by particle-assisted growth or the so-called VLS (vapor-liquid-solid) mechanism, which is disclosed in e.g. U.S. Pat. No. 7,335,908. Particle-assisted growth can be achieved by for instance use of chemical beam epitaxy (CBE), metalorganic chemical vapor deposition (MOCVD), metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), laser ablation and thermal evaporation methods. However, nanowire growth is not limited to VLS processes, for example the WO 2007/102781 shows that semiconductor nanowires may be grown on semiconductor substrates without the use of a particle as a catalyst. Nanowires have been utilised to realise devices such as solar cells, field effect transistors, light emitting diodes, thermoelectric elements, etc which in many cases outperform conventional devices based on planar technology.
Although having advantageous properties and performance the processing of nanowire devices was initially costly. One important breakthrough in this respect was that methods for growing group III-V semiconductor nanowires, and others, on Si-substrates has been demonstrated, which is important since it provides a compatibility with existing Si processing and non-affordable III-V substrates can be replaced by cheaper Si substrates.
When producing semiconductor nanowire devices comprising nanowires grown on a semiconductor substrate utilizing the above mentioned techniques a number of limitations are experienced:                an MOCVD system is a complex vacuum system, which significantly contributes to the production cost for the device;        growth is performed in batches, with inherent variations between individual batches;        growth of a large number of nanowires over a large surface yields variations between nanowires in the same batch;        the nanowires are grown on substrates which needs to withstand temperatures of 400-700° C.; and        to align nanowires in the vertical direction, or any other direction, on the semiconductor substrate requires controlled epitaxial growth.        